Optical parametric oscillators (OPOs) are frequently used as tunable infrared light sources. Conventionally they are realized by an optically pumped laser cavity including a non-linear crystal. The parametric oscillation is effected by irradiating the nonlinear crystal with an intense pump beam having a frequency ν3. In the nonlinear crystal quantum correlated photons of frequencies ν1 and ν2 are generated spontaneously by parametric scattering according to the relation ν3=ν1+ν2, wherein ν1 is the photon frequency. The generated modes are denoted as signal and idler modes.
Conventional OPOs usually require a lengthy and inconvenient initial alignment procedure and during their operation a continuous feedback control of the cavity length in order to compensate for cavity length fluctuations. Furthermore, in OPOs of this conventional type signal and idler photonic emissions comprise strongly unequal intensities.